The invention concerns a product feed control of a cylinder mill, especially a cylinder grain mill with an electric sensor, a product feeder with an adjustable drive for the feed, and a process to control such a cylinder mill.
To control the product feed of a cylinder grain mill, the set conditions must be maintained, i.e.:
Even product distribution over the entire length of the rollers,
The amount of product flowing to the cylinder mill must be processed within permissible tolerances, and the fluctuations in supply must be compensated as much as possible,
When the product supply is interrupted, the product feed to the milling rollers must be stopped quickly, and the milling rollers must be disengaged.
For decades, basic elements such as distribution rollers and feed rollers have proven themselves along with mechanical probes as sensors for finely controlling the feed to the milling rollers. The use of capacitive sensors in such probes in the feed area is prior art in WO 93/06928. The same is true for infrared sensors. A minimum of two sensors is required, and usually more than 6 measuring points are provided. The momentary setting of the product amount being fed to the milling rollers can be controlled by regulating the speed of the feed rollers or the feed gap between a feed gate and the feed roller which is also termed segment adjustment. In practice, both speed control and segment adjustment are used. Such a speed control is e.g. described in DE-U-8614505. A segmental displacement of a product feed control is described in EP-A-38054. In the feed area of a cylinder mill is a vertical probe that has numerous angled rods. As is the case with mechanical scales, an analog mechanical signal is generated by various transmission members during the product flow that is converted into an analog pressure control signal in a downstream pneumatic value. This forms the input signal of a servo control for setting the product feed and/or the engagement/disengagement of the grinding drums.
A similar solution is found in GB-A-2103389 where the vertical, height-adjustable probe has several plate-shaped arms that are perpendicular to the product flow direction.
Such pneumatic mechanical feed controls are involved and friction-dependent. If the metered product has the constitution of flour or farina, segmental displacement is preferred. If the products are flakes such as whole-corn meal, speed control is often superior. Since the feed control design is predetermined for each cylinder mill and the mills are generally not converted afterward, individual jobs may not have the correct feed control. As described in greater detail in EP-B-515596, grinding is the heart of each mill, and controlling the product feed is particularly important. It has therefore been suggested that the feed control be provided with a first mechanical signal generator for a digital signal and a second mechanical signal generator for an analog signal to provide satisfactory stabilization. Such a mechanical system is not very costeffective, comparatively involved and it absorbs friction that changes and hence influences the measuring result.
Furthermore, such a mechanical system tends to get dirty and allows products to clog due to bridge formation.
The invention is therefore based on the problem of eliminating the described disadvantages and creating a simply-designed product capture system at the inlet that can be easily integrated in an automatic feed control. Another problem of the invention is to develop a procedure to control a cylinder mill, especially the product feed.
The product feed control is characterized in that the measuring signal is generated with just one sensor at the inlet. An elastic measuring strip is preferable. In the procedure according to the invention, a control signal is generated that controls the engagement and disengagement of the grinding rollers or basic positions of the product feed system. The sensor senses a static force component from the product flow proportional to the product amount above, and a dynamic force component depending on the composition and flow properties (especially the rate) of the product.
Changing friction coefficients from contact with the product largely do not Influence the measuring signal. There is practically no soiling or corresponding influence on the control signal.
The main advantage of the solution according to the invention is the technically simple product detection and easy adaptation to existing feed control systems such as in EP B 515596. In addition, there are no mechanically moving parts that can get dirty.
The shut-off/on point can be determined with just one sensor, and the feed control can be governed by the same received signal.
Using amplification in the prior-art electronic component, only a small force component of the product flow is necessary, and only a small amount of friction arises from the small sensor that is installed.